import tensorflow as tf
import os
os.environ['TF_CPP_MIN_LOG_LEVEL']='2'

zero = tf.zeros([3, 4], tf.float32)

a = tf.cast([[1,2,3], [4,5,6]], tf.float32)

b = [[1,2,3], [4,5,6]];
c = [[7,8,9], [10,11,12]]
d = tf.concat([a, b], axis=0)
e = tf.concat([a, b], axis=1)

with tf.Session() as sess:
    print(zero.eval())
    print(a.eval())
    print(d.eval())
    print(e.eval())